There was a sad little bad-mannered outburst of slow handclapping before the opening of Deathtrap last night, led by a few critics in the front stalls because the curtain was nearly 20 minutes late going up. This seemed a bit unreasonable on a day of utter travel chaos caused by the Tube strike and a severe seating mix-up in the back half of the stalls.

The front of house staff were struggling, which didn't stop the Daily Telegraph's Charles Spencer rising angrily from his seat to give a few of them a small piece of his mind. Not a good start to the evening.

Still, the show came down well before 10pm, at 9.45pm in fact, which left oodles of time for the overnight reviewers to file copy while the rest of the audience were treated to champagne on the house. It's quite normal for a West End first night to start ten, sometimes 15 minutes late, but it can be exasperating for critics with deadlines. The Times' Irving Wardle used to start cracking his knuckles and then shout "Shop!" if things were really slow.

And there's always that sense of alienation among critics who are there to do a job while the rest of the audience is on hand merely to enjoy themselves and bask in each others' celebrity.

It sure was a good night for that little sport. On my small patch of stalls alone I was surrounded by Rafe Spall in some dashing red braces, Damian Lewis with his hat on back to front, his wife Helen McCrory, yachtswoman and thriller writer Clare Francis, the amazing Barbara Windsor, her agent Barry Burnett, Michael Ball and Cathy McGowan, Mark Almond and, further along Row G, A A Gill and Stephen Fry, though I don't think they were talking to each other.

It was a really good turn out. In the foyer at the interval I found Michael White, the producer of Sleuth all those years ago, and Millie Rowland, widow of Toby Rowland, one of the great West End figures of yore, who had come up from Brighton with actors' agent Simon Beresford; Simon astonished me by saying he had never spoken to a critic in an interval before.

Well, there's a first time for everything. Even for seeing Deathtrap. Like Sleuth, to which it is inferior, Deathtrap isn't really a thriller at all. It's a spoof, with a few manufactured thrills and spills and some fairly funny lines.

It is extremely well crafted and, save for a bad dip in the second act, moves at a cracking pace in Matthew Warchus' production. As Simon Russell Beale's character, Sidney Bruhl, says of his protege's brilliant first effort,"Not even a good director could hurt it."

On the other hand, can you believe any of it? Specifically, that Simon Russell Beale is married to a miscast Claire Skinner, or that he has any sort of plausible crush on Jonathan Groff, his sidekick and nemesis?

Russell Beale shows as much relish as acid distaste for his witty lines. "Nothing recedes like success" is punted into the stalls, gets its laugh and is matter-of-factly reclaimed as a possible line for the new play. And when Sidney's attorney, asked about his daughter at college, tells Russell Beale that "Kathy loves Vasser," the reply zings back, "And Vasser versa, I'm sure."

This must be one of the worst puns ever heard on the West End stage, and the mixture of triumph and shame with which Russell Beale releases it is a joy to behold.